There are two main types of logistical models used for long-term performance prediction of autonomous power systems: time series and probabilistic. Time series models are more common and are more accurate for sizing storage systems because they are able to track the state of charge. However, the computational time is usually greater than for probabilistic models. It is common for time series models to perform 1-year simulations with a 1-hour time step. This is likely because of the limited availability of high resolution data and the increase in computation time with a shorter time step. Computation time is particularly important because these types of models are often used for component size optimization which requires many model runs. This thesis includes a sensitivity analysis examining the effect of the time step on these simulations. The results show that it can be significant, though it depends on the system configuration and site characteristics. Two probabilistic models are developed to estimate the temporal resolution error of a 1-hour simulation: a time series/probabilistic model and a fully probabilistic model. To demonstrate the application of and evaluate the performance of these models, two case studies are analyzed. One is for a typical residential system and one is for a system designed to provide on-site power at an aquaculture site. The results show that the time series/probabilistic model would be a useful tool if accurate distributions of the sub-hour data can be determined. Additionally, the method of cumulant arithmetic is demonstrated to be a useful technique for incorporating multiple non-Gaussian random variables into a probabilistic model, a feature other models such as Hybrid2 currently do not have. The results from the fully probabilistic model showed that some form of autocorrelation is required to account for seasonal and diurnal trends. / Graduate

Penetration of renewable energy generators into energy systems is increasing. The intermittency and variability of these generators makes supplying energy reliably and cost effectively difficult. As a result, storage technologies are proposed as a means to increase the penetration of renewable energy, to minimize the amount of curtailed renewable energy, and to limit the amount of back-up supply. Therefore, methods for determining an energy system’s storage requirements are being developed. This thesis investigates and details four existing methods, proposes and develops a fifth method, and compares the results of all five methods. The results show that methods which incorporate cost, namely the Dynamic Optimization and the Abbey method, consistently yield the most cost effective solutions. Under excellent renewable energy conditions the results show that the cost-independent methods of Korpaas, Barton, and the Modified Barton method produce solutions that are nearly as cost effective but have greater reliability of energy supply than the Dynamic Optimization and Abbey solutions. This thesis recommends a new path of research for the Modified Barton method: the incorporation of cost through the confidence level. This thesis also recommends the development of new sizing methods from various aspects of the methods presented. / Graduate

Losses for wake effects in offshore wind farms represent about 10% to 20% of the park annual energy production. Several analytical wake models have been developed and implemented to predict the power deficit of a wake-affected wind turbine. Validating and parameterizing the wake models available in the industry is essential to better predict the wake losses and thus maximize the energy yield of future offshore developments. In this study, a wake model validation is undertaken for the three models available in the commercial software WindSim. Data from Horns Rev wind farm is used to that purpose. Next, the models that show the best agreement with the observations are parameterized to better describe the power losses of a future offshore wind farm at Bockstigen. To finish with, an optimization sensitivity study is carried out and a final optimal layout is determined according to the seabed depth.

Concerns over climate change impacts, goals to increase environmental sustainability, and questions about the reliability of fuel supply have led several countries to pursue the goal of increasing the share of renewable energy sources in their electricity grid. Portugal is one of the leading countries for wind electricity generation. Wind diffusion in Portugal started in the early 2000’s and in 2013 wind electricity generation accounted for more than 24% (REN 2013b). The large share of wind in Portuguese electricity production is a consequence of European Union (E.U.) mandates and national policies, mainly feed-in tariffs. Discussions on the appropriate policy design and level of incentive to promote renewable energy adoption and meet further renewable capacity goals are ongoing in Portugal, namely in what concerns the level and duration of feed-in tariffs that should be provided to independent power producers. This, in turn, raises the question of whether the past feed-in tariff levels were well designed to achieve the goals of a larger penetration of renewables in the Portuguese grid. The policies to induce wind adoption have led to a growth in wind installed capacity and share of electricity generated by wind in Portugal from less than 1% in 2000 to approximately 24% in 2013, but questions arise on their cost-effectiveness and whether alternative policy designs would have led to the same goal. vi The Portuguese wind feed-in tariffs are a guaranteed incentive which has varied between $85- $180/MWh over the last 20 years (ERSE 2011), and remained approximately constant since 2001 at $101/MWh. They are currently guaranteed for 20 years of production or 44GWh of electricity generation per MW installed (Diário da República 2013) - the longest period among countries with high wind electricity share. They do not incorporate any digression rate besides inflation, and are guaranteed for every unit of electricity fed to the grid. There are no power plants that have already been decommissioned despite being in operation for more than 20 years, favoring from new, detailed and hard-to-follow agreements in the legislation. All wind parks that are currently in operation have received feed-in tariffs since they connected to the grid, and are expected to keep receiving them at least until December 2019, and up to December 2036 - depending on year of connection and agreement under the most recent legislation (Diário da República 2013). The 2020 renewable energy goals in Portugal include having 6.8 GW of installed wind capacity, which implies the connection of 2 GW in the next years. If no further grid investments are made and wind capacity increases up to 100 MW to the connection point that we analyze, total annual electricity spill is likely to range the 20% to 40%. If the connection grid policy is designed to allow for wind spill, already ‘occupied’ connection points will be available to new entrants, lowering the total investment costs for new wind parks and increasing their profitability. This thesis is divided in three main parts: a first introductory section, a retrospective study of wind power in Portugal and a prospective analysis of the Portuguese wind power sector. The introductory section is a brief overview of the global renewable status, described in Chapter 1. Chapter 2 and Chapter 3 compile a retrospective study of wind power and the policies that have incentivized wind diffusion. We include in the discussion some references to the future wind vii power goals, but the results and policy recommendations are directed towards the existing connected wind power capacity. Chapter 2 is a qualitative piece that describes in detail the motivation behind the Portuguese wind power diffusion, the policy changes over the last 20 years and the mechanics of the remuneration mechanism, i.e. the feed-in tariff formula variables and the actors of the wind power sector. We compare the Portuguese feed-in tariff with other European feed-in tariff designs and conclude that the incentive is one of the highest in Europe, contributing to the current Portuguese electricity system deficit of about $2 billion. If feed-in tariffs keep being fixed and do not incorporate any market variation, and renewables are prioritized to meet electricity demand, feed-in tariff net support per unit of electricity might be higher when the wind blows the most because moments with high penetration of renewable power might be correlated with low market prices. We find that wind power penetration is correlated with net exports to Spain. This might result in a net cost to Portugal and a subsidy to Spanish electricity consumers per unit of electricity traded. In total terms, the resulting subsidy is higher when the wind resource is larger as well, as the total amount of electricity that is exported increases. In Chapter 3 we estimate the profits of wind power producers connected in Portugal between 1992 and 2010, and we recommend specific policy reforms that would lower spending in the form of wind feed-in tariffs. In particular, we assess four scenarios to decrease the level and/or period of the tariffs. We find that under the 2005 legislation - in which feed-in tariffs are granted for 15 years, all existing wind parks have positive NPVs varying between $0 and $12/MWh, when considering a 20-year lifetime. In fact, most of existing wind parks can stop receiving the feed-in tariff now (July 2014), and instead participate directly in the Iberian electricity market and still be profitable. Moreover, under the 2013 feed-in tariff reform that aims at decreasing the viii electricity system deficit, total spending will increase and wind parks will have larger profits than under the 2005 legislation. The motivation of keeping a high feed-in tariff comes from the need of liquidity that wind producers can provide immediately to the electricity system, which is required at this moment to comply with the E.U. economic agreements signed during the recession. Nevertheless, the environmental and energy dependency benefits of the Portuguese wind sector could have been achieved with as much as 25% less spending. Later on, we move to analyze future wind power additions. Chapter 4 compiles a prospective analysis of the wind power sector in Portugal. We focus on new wind parks that will connect to critical lines of the distribution grid in two regions of the country, as part of the national 2030 wind power goals. In particular, we assess the implications of a 100% guaranteed availability of grid power capacity. We find that from the investor perspective, it is more profitable to bear some risk of wind power curtailment, because of the avoided costs that would otherwise be incurred to upgrade the grid. We also find that since there is ample room in the distribution lines to connect more wind parks, very few grid upgrades can allow to highly increase the distributed wind capacity with a low risk of wind curtailment. Moreover, even in scenarios with ‘high curtailment’ of 5% to 20%, projects are profitable. Thus, the Portuguese government should consider a policy where the guaranteed feed-in would be removed, and further assess the possibility of limiting profitability of the existing and new wind projects by introducing curtailment. This work compiles two perspectives: first, a temporal perspective, in which past and future assessments of wind power diffusion are described. Second, a perspective on policy characterization, in which we present an assessment of two characteristics in the feed-in tariff design: the level/period of the tariff and the conditionality of prioritizing wind power over fossilix fuel resources with absence of risk of wind power curtailment. The level and period-related policy recommendations are considered for the existing wind parks, and are addressed mainly in Chapter 3. Considerations about grid capacity and introducing a risk of wind power curtailment are considered for subsequent wind power capacity additions, and are mainly considered in Chapter 4. In addition, notice that Chapter 3 focuses on avoiding excessive profitability of wind power parks while in Chapter 4 we analyze wind and grid capacity additions under the perspective of wind investors. Nevertheless, as we also find in Chapter 4 that profits are excessive, we do make recommendations that limit wind investor’s revenue. Portuguese decision maker should give serious consideration to revisions to the Portuguese feed-in tariff policy design. Most of the existing Portuguese wind parks to not need a feed-in tariff to be profitable. A value associated with the risk of wind power curtailment for subsequent additions should be incorporated in future policy design. We expect that this work will contribute to the Portuguese renewable policy in particular in light of Portugal’s 2020 and 2030 wind power goals.

One of the key points to reduce the world dependence on fossil fuels and the emissions of greenhouse gases is the use of renewable energy sources. Recent studies showed that wind energy is a significant source of renewable energy which is capable to meet the global energy demands. However, such energy cannot be harvested by today’s technology, based on wind towers, which has nearly reached its economical and technological limits. The major part of the atmospheric wind is inaccessible to the conventional wind turbines and wind at higher altitude is the major source of potential energy which has not been fully exploited yet. The thesis paper has presented a study aimed to devise a new class of wind generator based on extracting energy from high altitude wind.A brief theoretical study is presented to evaluate the potential of an innovative high altitude wind power technology which exploits a tethered airfoil to extract energy from wind at higher altitude. Among the various concepts proposed over last few decades, a kite power system with a single kite is selected for the design purpose.The designed ground station is an improvisation over existing prototypes with an energy reservoir for having a continuous power output. A flywheel is used as the energy storage system which stores the extra energy during traction phases and supplies it during recovery phases and thus giving a continuous power generation regardless of the kite’s motion and keeping the rotor speed in a permissible range defined by the design constraints. Manufacturability of the structure, availability of the components, safety and maintenance criteria have been taken into account while building the ground station CAD model.A dynamic simulation model is developed to investigate the power transmission system of the kite power unit which reflects the torque, speed and power behaviour of the modelled ground station driveline. The functionality of the designed model for the selected concept is tested with several numerical and graphical examples.

Wind power installations are growing rapidly throughout the world due to environmental concerns associated with electric power generation from conventional generating units. Wind power is highly variable and its uncertainty creates considerable difficulties in system operation. Reliable operation of an electric power system with significant wind power requires quantifying the uncertainty associated with wind power and assessing the capacity value of wind power that will be available in the operating lead time. This thesis presents probabilistic techniques that utilize time series models and a conditional probability approach to quantify the uncertainty associated with wind power in a short future time, such as one or two hours. The presented models are applied to evaluate the risk of committing electric power from a wind farm to a power system. The impacts of initial wind conditions, rising and falling wind trends, and different operating lead times are also assessed using the developed methods. An appropriate model for day-ahead wind power commitment is also presented. Wind power commitment for the short future time is commonly made equal to, or a certain percentage, of the wind power available at the present time. The risk in meeting the commitment made in this way is different at various operating conditions, and unknown to the operator. A simplified risk based method has been developed in this thesis to assist the operator in making wind power commitments at a consistent level of risk that is acceptable to the system. This thesis presents a methodology to integrate the developed short-term wind models with the conventional power generation models to evaluate the overall operational reliability of a wind integrated power system. The area risk concept has been extended to incorporate wind power, evaluate the unit commitment risk and the well- being indices of a power system for a specified operating lead time. The method presented in this thesis will assist the operator to determine the generator units and the operating reserve required to integrate wind power and meet the forecast load for a short future time while maintaining an acceptable reliability criterion. System operators also face challenges in load dispatch while integrating wind power since it cannot be dispatched in a conventional sense, and is accepted as and when present in current operational practices. The thesis presents a method to evaluate the response risk and determine the unit schedule while satisfying a specified response risk criterion incorporating wind power. Energy storage is regarded as an effective resource for mitigating the uncertainty of wind power. New methods to incorporate energy storage with wind models, and with wind-integrated power system models to evaluate the wind power commitment risk and unit commitment risk are presented in this thesis. The developed methods and the research findings should prove useful in evaluating the operating risks to wind farm operators and system operators in wind integrated power systems.

Thesis (M.E. (Elec.) (Hons.)) -- University of Western Sydney, 2002. / "Submitted for the Master degree of Electrical Engineering (Honours)" Includes bibliographical references (leaves 131-136).

Diss. (sammanfattning) Stockholm : Tekn. högsk., 2001. / Härtill 7 uppsatser.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 12, 2008) Includes bibliographical references (p. 64-66).

Thesis (M.A.) -- University of Montana, 2008. / Title from author supplied metadata. Description based on contents viewed on July 15, 2009. Includes bibliographical references.